Had my Metz M1 repaired by my tyre man. He's very picky about the kind of puncture he's willing to plug.
Metzeler also state that under certain circumstance their tyres can be repaired.
Metz Q&A
It's plugged from the inside and I got him to put it on my spare rear which I have used for the winter with no problems.
Now need some new hoops for the summer as I'm riding the bike much harder, but will put the spare wheel back on next winter.